The invention relates to seal assemblies.
Seal assemblies are widely used between rotating and stationary elements. For example, a steam turbine typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. Steam leakage, either out of the steam path or into the steam path, from an area of higher pressure to an area of lower pressure may adversely affect the operating efficiency of the turbine. Accordingly, seal assemblies are provided between the rotor and surrounding casing (stator) for minimizing steam leakage.
A seal assembly is typically attached to the rotor or casing, and is, during steady state operation of the turbine, either in a friction fit or situated so as to provide a small gap between the rotor and the casing. It is desirable for seal assemblies to have long useful lives so as to minimize the need for maintenance and repair. However, during transient operations, such as start up or shut down of the turbine, the rotor may deflect towards the surrounding seal and therefore cause undesirable rubbing. Accordingly, seal assemblies may become adversely worn and thus suffer from a shortened useful life and reduced sealing effectiveness. Furthermore, seal assemblies are also subject to differential thermal expansion and contraction movement with the rotor during transient operation which can also cause undesirable rubbing.
It would be desirable to have an improved seal assembly and sealing method to accommodate relative transient movement of the rotor and stator.